[PATCH v2] tty: serial: atmel: add earlycon support

[Michael Walle]

Add early console support which relies on the bootloader for the
initialization of the UART.
Please note, that the compatibles are taken from at91-usart MFD
driver.

Signed-off-by: Michael Walle <michael at walle.cc>
---
 drivers/tty/serial/Kconfig        |  1 +
 drivers/tty/serial/atmel_serial.c | 24 ++++++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index 0e5ccb25bdb1..407a98ec0791 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -139,6 +139,7 @@ config SERIAL_ATMEL_CONSOLE
 	bool "Support for console on AT91 serial port"
 	depends on SERIAL_ATMEL=y
 	select SERIAL_CORE_CONSOLE
+	select SERIAL_EARLYCON
 	help
 	  Say Y here if you wish to use an on-chip UART on a Atmel
 	  AT91 processor as the system console (the system
diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
index 2d09a89974a2..73d43919898d 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -2673,6 +2673,30 @@ static struct console atmel_console = {
 	.data		= &atmel_uart,
 };
 
+static void atmel_serial_early_write(struct console *con, const char *s,
+				     unsigned int n)
+{
+	struct earlycon_device *dev = con->data;
+
+	uart_console_write(&dev->port, s, n, atmel_console_putchar);
+}
+
+static int __init atmel_early_console_setup(struct earlycon_device *device,
+					    const char *options)
+{
+	if (!device->port.membase)
+		return -ENODEV;
+
+	device->con->write = atmel_serial_early_write;
+
+	return 0;
+}
+
+OF_EARLYCON_DECLARE(atmel_serial, "atmel,at91rm9200-usart",
+		    atmel_early_console_setup);
+OF_EARLYCON_DECLARE(atmel_serial, "atmel,at91sam9260-usart",
+		    atmel_early_console_setup);
+
 #define ATMEL_CONSOLE_DEVICE	(&atmel_console)
 
 #else
-- 
2.30.2